Method of manufacturing electrically conductive membranes and the like



United States Patent O METHOD OF MANUFACTURING ELECTRICALLY CONDUCTIVE MEMBRANES AND THE LIKE John Thacher Clarke, Newton Highlands, Mass., assignor to Ionics, Incorporated, Cambridge, Mass., :1 corporation of Massachusetts No Drawing. Application December 5, 1951, Serial No. 260,080

11 Claims. (Cl. 18--58) This invention relates to a method of making elec 1953, describes synthetic polymeric materials in, the,

form of hydrous gels which may be formed into such large dimensioned structures as membranes, tubes, rods, vessels and the like. These materials, like ion exchange resins, include in their polymeric structure dissociable ionizable radicals, one ionic component of which is fixed into or retained by the polymeric matrix and at least one component of which consists of a mobile and replaceable ion electrostatically associated with the fixed component. The ability of the mobile ion to be replaced, under appropriate concentration conditions, by ions of the same charge, imparts ion exchange characteristics to these materials.

More important, however, is the effect the fixed radicals have on the electro-conductive properties of these materials. The fixed ions possess charges which attract ions of opposite charge and repel ions of like charge. Under the influence of an electric field, ions charged like the mobile ions may be caused to permeate the material exclusively of ions of the opposite charge, which are repelled. These materials are accordingly electrically conductive and selectively permeable. The above mentioned application of Juda and McRae describes a method of manufacture wherein the polymerizable ingredients are reacted to the final stage of polymerization which is to be etfected while maintained in an aqueous solution under conditions preventive of evaporation of water. Here it was believed that the presence of water was effective in causing proper orientation of the ion exchange groups in dissociable position, by providing dissociable conditions during the polymerization and assuring that the ion exchange groups of the final polymer were dissociably retained. It has now been found that the polymerization may be carried out in the presence of organic solvents, and in the absence of water. The present inveniton comprises a method of manufacturing polymeric solid material of the general characteristics of those described by Juda and McRae and provides a method of manufacturing such materials wherein the polymerizable ingredients are reacted to the final stage of polymerization which is to be effected while maintained in solution in an organic solvent. By this means, polymerizations can be carried out which are inhibited or prevented in aqueous solution, and thereby electrically conductive structures may be manufactured by the present method which are not obtainable by the method described by Juda and McRae. Frequently, it

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also happens that the presence of water during the polymerization causes that reaction to proceed at a rate which is too rapid for the formation of homogeneous coherent structures. Bythe present invention, it is often possible to select an organic solvent for the polymerizable ingredients in which the polymerization proceeds at a more convenient rate. For instance, when resorcinol, a polyalkylene polyamine, and formaldehyde are caused to condense in water, it is necessary to acidify the solution to slow down the rate of polymerization. However, these ingredients may be reacted in a solution of methanol without acidification, and the polymerization proceeds at a desirably slow rate.

The materials which may be manufactured by the method of this invention are not only electrically conductive and selectively permeable but are also mechanically durable, so that they may be formed into selfsustaining structures and are substantially hydraulically impermeable under ordinary pressure differentials, so that they may be used effectively as hydraulic separators. These materials may be used in dialysis and electrodialysis apparatus where advantage may be taken of their selectively permeable and highly conductive prop erties. Several such arrangements are described in the above identified application of Juda and McRae.

This invention is concernedin general with the preparation of synthetic organic polymeric structures of extreme insolubility and which are in the form of solvated gels containing active ion exchange groups. Accordingly, the polymeric solvated structures are highly crosslinked, at least to the extent necessary to impart the required degree of insolubility and to preventundue volume changes, often accompanied by disintegration, when contacted with other liquids. Generally, the extent of crosslinking for this purpose is obtained by using at least 20 mol per cent and up to 100 mol per cent of crosslinking compounds on the total mols of polymerizable compounds. Preferably the extent of crosslinking is from 30 to mol per cent. In the appended claims, the term a highly crosslinked polymeric matrix is intended to mean polymeric structures obtained by the use of at least 20 mol per cent and up to mol per cent of crosslinking compounds on the total of all polymeric compounds. Ion exchange groups are incorporated in the polymeric matrix eitherby utilizing polymerizable ingredients which include dissociable ion exchange functions or by reacting the polymeric material after polymerization to combine ion exchange functions into its polymeric matrix. It is contemplated that in most applications of materials prepared in accordance with this invention, they will be used in treating solution such as aqueous solutions, the solvent of which is not present in their gel structures during preparation. A feature of the process of this invention is the replacement of the gel solvent by other liquids, most commonly, water, in order to avoid contamination of the solutions to be treated by the gel solvent.

According to the process of this invention, monomeric or partially polymerized components of precursors of highly cross-linked electrically conductive ion permeable polymers are caused to polymerize while maintained in solutions in a suitable organic solvent under conditions preventive of substantial evaporation of the solvent and preferably, in physical surroundings, such as casts or molds which predetermine the shape of the polymerized structures. Polymerization is effected by any of the well-known expedients, for instance, heat, pressure, and catalytic accelerators and is continued until an insoluble, intusible gel isformed substantially throughout the volume of solution. The active or potentially-active ion exchange groups may be fixed in one or more of the monomeric precursors or in the partially polymerized precursors; or the ion exchange groups may be included or segregation. Y

be allowed to lose their solvent content as lay-evaporation Polymeric organic materials of both the addition and condensation type may be advantageously prepared by the process of this invention provided that there may be imparted to the material the requisite amount of cross linking. For instance, addition-type polymers include copolymers of divinyl benzene or similar diolefinic compounds with any one or more of the following cornpounds: acrylic acid, methacrylic acid, acrylic esters, methacrylic esters, styrene, maleic anhydride, styrene parasulfonate esters, styrene para-sulfonic acids, para-chloromethyl styrene, paradialkylamino] styrene, dialkyl paravinyl benzylamine, trialkyl para-vinyl benzyl ammonium salts, N-alk yl vinyl pyridinium salts, acrylonitrile vinyl acetate, vinyl chloride, allyl alcohol, vinylidinc chloride, and similarpolymerizable compounds. The divinyl benzene is included in these copolymerizations to provide for crosslinking across linear polymeric chains. Other diolefinic'compounds which may be used for this same purpose includedi-iso propenyl benzen'es and diallyl ether. The dimethacrylate esters of ethylene glycol or tetraethylene glycol'may'also be used but since they are esters, they are not as resistant to water as divinyl benzene, and tend to hydrolyze upon prolonged conta'c'cwith ,water.

Condensation type polymers may also be made according to the process of this invention and they include the condensation products ofaldehydes with any of the fol lowing compounds: phenol and substituted phenols; di-

hydroxybenzen'es, phloroglucinol; aniline and substituted anilines; metaphenylene diamine; melamine; urea; guanidine and guanidine derivatives; polyhydric phenols and polyalkylene polyamines; and kCtOllGS with amines.

In general the process of this invention may be applied to the formation of any highly crosslinlged polymeric matrixi in whichthe desired dissoci able ion exchange groups may be incorporated. Certain polymeric materials,'however, are inherently unstable in water, such as polyester structures which tend to hydrolyze; but this limitation does not preclude the formation with them of crosslinked polymeric gels having active ion exchange groups,

I ill e s r e h al hough m ny of th po mers i t ab v inher utly on n active ion exchan roup ny of the o ot e form ion f selecti ely p r m a c nd ti e. r ct res i h the latter ype ma eri ls involves the, step of incorporating ion vexchange groups into the polymeric matrix as shown in the examples.

By m in a i g is ol ed or dispe sed ondi i n hrou ho th poly e zation, her r sults a o d sc vated gel containing a continuous liquid (solvent) phase,

which retains the form of the dispersed liquid and which is'furtherrnore a coherent and homogeneous structure. The presence of this continuous liquid pha sei makes it possible to treat the solid gel structure with reactants which combine active ion exchange groups with the polymeric .material (that is, when it is necessary to implant ion exchange groups inpolymeric. structures which are wards, be reduced unlessreplaced withanother solv ating liquor, Permitting the solvating liquid content to become lower is likely to cause cracking of the structure or impairment of the electrical properties of the material. Although a minimum solvent content of 25 per cent has been found effective for the purpose of this invention, preferred embodiments include such larger amounts as do'not interfere with the physical structure of the solid. Structures including as much as 75 per cent of solvent have been found satisfactory.

By maintaining dissolved or dispersed conditions during the polymerization, the structures of this invention polymerize throughout the volume of solution to form a polymericmatrix which entrains the solvent, thus resulting in a solvated gel structure which is particularly suitable for the purposes of this invention. The volume of the solvent present during the polymerization has been found to determine or fix the equilibrium liquid content of the polymerized structure. That is, the gel, after drying and reswelling in the same or a different solvent, imbibes substantially the same volume of liquid as was present during polymerization. This is particularly useful since it is often advantageous to carry out the introduction of the ion exchange groups (where this is required) in' the presence of a solvent which is different, fromthat used in polymerization. The gel does, however; shrink when liquid is removed from it, as by evaporation (regaining nearly the same volume on resolvating, however) which indicates that the polymeric matrix of the gel is not rigid but is ratherof limited extensibility.

Ordinary'curing conditions in which the solvent is not present or in which it is allowed to escape or evaporate, do not result in the formation of continuous, coherent, or homogeneous structures which are appreciably selectively permeable and electrically conductive. Either a continuous resinous, dielectric results as is typified by the well known acrylate, styrene, melamine or phenolic mold-- ing rcsins,'or a fractured or particulate structure results which is typified by the granular ion exchange resins, for example, those described in U. 8. Patents 2,195,196; 2,340,110; 2,340,111; 2,106,486; 2,198,874; and 2,228,514.

The products produced in accordance with this invention when converted to the aqueous form have been found to have high electrical conductivities generally in excess of 5X10 ohm- CHl. They are substantially selectively permeable to ions of one sign or the other as indicated by the fact that in the standard concentration cell:

calomel sat? 0.1N mem- 0.01N calouicl i electrode KGl brane KOl bridge electrode bridge at 25 (1., a' characteristic concentration potential approaching an absolute value. of 55.1 millivolts may be measured, The ion exchange capacity. of thesematerials is desirably in excess of 0.3 milliequivalent per gram of solid material after correction hasbeen made for the solvent content and for reinforcing material if present. They possess hydraulic resistivities in excess of 100. atm, sec. Gill-7 (the pressure in atmospheres required to cause liquid to p rmeate acentimeter cube of the material at the rate of l cubic centimeter per second).

Structures may be formed in accordance with this invention by castingor molding (including compression molding) the solution of polymerizable components or partially polymerized. components. and causing polymerization in themolds-or casts, as by heating, while preventing the evaporation or escape of substantial amounts of solvent (for instance, by closing the molds or otherwise carrying out the polymerization under substantially saturated solvent conditions). In this WHY forms and structuresmay be prepared in any desired shape and size, including structures. having at least 1 dimension greater than 4inch, and which are accordingly far greater in size than structures in which conventional ion exchange materials have been made in the past. Reinforcing materials which do not interfere with the polymerization such as glass cloth, paper, or the like, be included in he molds or costs On the other h nd, hereinforc rs. m rial may be impr g ated w th the un olym nzed r partially polymerized solution and polymerization subsequently carried out under conditions which prevent the escape or segregation of solvent; q q

The selection of a suitable solvent in which any particular polymerization may be eifected, will, of course depend in part on the nature of the polymerizable ingredients-for the liquid must be capable of forming a solution or dispersion with them-and upon the effects of the solvent on the polymerization reaction which should be neither accelerated to too rapid a rate nor inhibited to too slow a rate by the solvent. Furthermore, since the solvent content must be. maintained during polymerization, the solvent must not enter into the polymerization reaction lest it be converted to resinous structures and cease to exist as a liquid phase. In general, satisfactory results may be obtained with such solvents as the lower aliphatic alcohols; the saturated ethers, including dioxane; saturated halogenated aliphatic liquids, such as acetone; and liquid aromatic hydrocarbons such as toluene; except that polymerizations which proceed according to the free radical mechanism should not be carried out in the presence of phenols. r

The rate of polymerization depends, in part, upon the concentration and nature of the solvent andcatalysts present, and upon the temperature of the polymerization, and should beso controlled by methods well known to the art as to allow convenient casting of the polymerizable solution and to prevent undue temperature increases which may result in the escape of solvent vapor bubbles by the heat of polymerization. Suitable proportions of catalysts and conditions of polymerization in particular applications are illustrated in the examples. In general, best results are obtained when the nature and concentration of catalysts and the temperature are such as to require at least one hour for the completion of polymerization;

If desired, the mixture of polymerizable ingredients may be partially prepolymerized before casting. This results in an increase in the viscosity of the solution and may be desirable in some cases to facilitate casting.

After polymerization, it is generally desirable to convert the solid polymeric gel structure to the hydrous gel form. If the solvent of polymerization is water-miscible, the gel need only be leached repeatedly in water until the solvent is extracted and replaced by water. If the .solvent is not water-miscible, it may be conditioned for water by first leaching the gel in a solvating liquid which is mutually miscible with both water andthe solvent, thus to convert the gel to a water-miscible-liquid form. Inasmuch as the solid structure of this invention are contemplated as having the greatest utility in the hydrous gel form, it is generallypreferable to select a watermiscible solvent for the polymerization if this is possible.

It has also been found that it is frequently possible to replace a water-immiscible liquid in. the, gel with water simply by immersingthe gel in water. It appears that the afiinity of the ion exchange groups for water is sufficiently great to cause the water to displace the waterimmiscible-liquid from the gel.

It is apparent from the foregoing that this invention pro vides a process of preparing a solvated gel having a polymeric solid phase. Selective permeability and electrical conductivity are imparted to the gel structure by providing ionic constituents such as are present in ion exchange resins, in the polymeric matrix. These constituents include any ionizible group, one component of which upon dissociation is incorporated into the polymeric matrix while the other consists of a mobile active ion. For example, a cation-permeable structure includes negative ions such as carboxylic or sulfonic, in the polymeric matrix, with mobile cations such as hydrogen, sodium, and the like associated therewith. An anion permeable structure, on the other hand, includes positive ions such as primary, secondary, or tertiary amino groups or quaternary ammo nium groups in the polymeric matrix, with mobile anions, such as hydroxyl, chloride, and the like associated with sulfonic acid, or formaldehyde, resorcinol, and a poly- Alternatively, the ionic groups may i incorporate sulfonic acid groups.

3 methyl sulfate.

or be dissolved in a suitable liquid, so that they do not solvates the gel.

them. These ionic groups are noted to have dissociation constants over 10- i It has been found that there should not be more than 4 milliequivalents of ion exchange groups incorporated in the polymerized structure for each mol of crosslinking agent and not less than 1 equivalent of ion exchange groups for each 10 mols of monomeric constituents.

The ionic groups may be present in the polymerizable ingredients from which polymeric gels are made, as in the case of the polymerization of formaldehyde and phenol alkylene polyamine. be incorporated in the polymeric matrix after the gel is formed. For instance, a copolymer of divinyl benzene and styrene may be formed which is thereafter sulfonated to Or vinyl pyridine and divinyl benzene may be copolymerized (to form a structure which has the ion exchange properties of a Weakly basic anion exchange resin) and thereafter quaternized to the quaternary ammonium form by treatment with di- If the ionic groups are to be incorporated in the polymeric matrix after polymerization and the formationof the solid gel structure, it is desirable that the solvatingliquid content of the solid structure be not reduced during the treatment; the same precautions against the net escape of solvent should be followed then as during the polymerization, least fracturing and/ or impairment of the electrical and mechanical properties result. Thus reagents used to treat the solid gel should either comprise 1 second liquid. This solventsubstitution. may be accon plished by leaching in the second solvent. Preferably the solvents to be interchanged are miscible; but if they are not one may first leach the structures in a solvent miscible with both liquids.

Solvent substitution is often advantageous particularly if the ion exchange groups are to be introduced after polymerization, for example, by the sulfonation of poly merizates of divinyl benzene and styrene. Solvent substitution permits the use of one solvent particularly suitable for the polymerization and of a second solvent which is well suited for the introduction of the active exchange groups. On the other hand, the reagent active in the introduction of exchange groups may be dissolved in a solvating liquid which is different from the one which On the other hand, the active reagent may itself be a suitable solvating liquid.

It is found that a product having improved mechanical properties is often obtained if the polymerized structure is leached-in a solvating organic liquid. This leaching apparently removes unpolymerized and low molecular weight constituents and is of greatest value when the exchange groups are added or formed after polymerization.

It has beenfound that the permissible ratio of equivalents of ion exchange groups per mol of crosslinking agent may be increased to as much as 6.0 or alternatively the amount of crosslinking may be decreased to as little as 20 mol per cent of the total polymerizable material provided a suitable structural reinforcing medium is used. This medium should have a tear strengthof at least 50 grams for each millimeter of thickness, a void volume of at least 50 per cent, and should have about as good chemical and heat resistance as the polymer. Generally, it is found that the reinforcing material should constitute at least 5 per cent but not more than 50 per cent by weight of the solvated structure. If less than 5 per cent is used there will be no appreciable increase in tear resistance and if more than 50 per cent is used, the desirable electrochemical properties will be seriously reduced.

Materials which are suitable for reinforcing the structures of this invention are glass filter cloth (such as National Filter Media Companys G-210), polyvinylidene chloride screen (such as Chicopee Manufacturing Com panys 15 x 18. Lumite screen), glass paper (such as Naval Research Laboratorys. Type AAA manufactured by Glass Fibers, Incorporated), treated cellulose battery paper (such as that manufactured by Dewey and Almy Chemical Company), polystyrene-coated glass fiber mat (such as that manufactured by Owens-Corning Fiberglas Corporation), and polyvinyl chloride battery paper (such as Electric Storage Battery Companys Porrnax) and the like.

Thefollowing examples have been selected for purposes of illustration and are not presented to suggest limitations not previously described and not included in the appended claims.

Example l.-Copolymer of divinyl benzene and maleic I anhydride In 200 cc. of peroxide free dioxane were dissolved 98 gram (l'mol) of maleic anhydride and 108 cc. of inhibitorfree 40-50 per cent divinyl benzene of commerce (by actual analysis containing 44 mol-per cent of divinyl ben- Example 2. S.'llf0lulfd eopolymer of divinyl benzene and styrene A solution was prepared containing 50 parts by weight of 50-60 per cent divinyl benzene of commerce (containing by actual analysis '53 mol per cent of divinyl benzene and about 40 mol per cent ethyl vinyl benzene) and 50 parts by weight of toluene and 0.3 part of benzoyl peroxide. The mixture was cast between two glass plates on a reinforcing material of glass cloth. The casts were heated at 80. C. for three hours under non-evaporative conditions. The casts were then cooled to room temperature, leached in ethylene chloride, andplunged into 96.5

per cent'sulfuric acid containing 0.1 per cent silver oxide. The polymerized structures were heated in the sulfuric acid at 90 C. for fifteen hours. After cooling, the sulfonated polymer was leached with water and subsequently equilibrated with l N sodium chloride solution. The structures were then leached with water until free of chloride. The electrochemical properties arelisted in Table 1.

Example 3. Plymers of resorcinol, phenol, sulfuric acid,

' and parafornmldehyde A 55 part by weight portion of resorcinol and 47 parts of phenol were melted together at a temperature of 100 C; and then cooled to 60 C. at which time 103 parts of 96 per cent sulfuric acid wereadded; The temperature was raised by this addition to 105 C. Over the course-of twenty minutes, the sulfonated mixture-was allowed to cool to 30 C. and40 parts of methanol were added. A

solution of 50 parts of paraformaldehyde in 100 parts of methanol was cooled to a temperature of -l0 C. The sulfonate solution was addedtothe cold paraforrnaldehyde solution with stirring. The addition was done slowly over the course of 30 minutes while maintaining the tempera ture between 0 C. and '5 C. The'resulting liquid was cast between two glass plates on a reinforcing material of glass cloth. It was then cured at. 60 C. for thirty hours under non-evaporative conditions. After curing, the casts were leached in distilled water and subsequently equili- Example 4.-P0lymer 0f resorcinol, diethylene triamine and parajormaldehyde A solution of 55 parts of paraformaldehyde in 110 parts of .methanol was added to 51.5 parts of diethylene triamine-boiling range, 200404 C.-disso'lved in 74 parts of methanol. The mixture was cooled to 5 C. and 55 parts ofiresorcinol in solid form were" stirred into the mixture. The temperature was'allowed to rise slowly to dissolve the resorcinol. When the resorcinol was dissolved, the liquid was cast between two glass plates on a reinforcing material of glass cloth. The casts were then cured at 60 C. for thirty hours under non-evaporative conditions. The resulting membranes were leached with distilled water, equilibrated with 1 N hydrochloric acid and then leached with distilled water to a pH of 3.5. The electrochemical properties are listed in Table I.

Example 5.-P0lymer of quaternizea' Z-vinyl pyridine and divinyl benzene To 36 cc. of 2-vinyl pyridine (0.34 mol) containing 0.1 per cent hydroquinone, dissolved in 40 cc. of iso-propanol andwarmed to 55 C. was added 36 cc. dimethyl sulfate (0.36 mol) at a rate such that the temperature did not exceed About ten minutes were required and the reaction'rnixture was occasionally cooled. The mobile solution was then cooled to room temperature;

To this solution was added 27 cc. of divinyl benzene (which containedby actual analysis 76 mol per cent of'divinyl benzene in a solution of ethyl vinyl benzene). The resulting mixture was then cast between two glass plates on reinforcing material of glass cloth. Care was taken to prevent the inclusion of bubbles. The casts were heated.

at'80 C. forthree hours, cooledto room temperature and then leached. with methanol, washed with water, equilibrated with 1 N sodium chloride solution and'then thoroughly leached with water. The properties of the resulting structure are given in Table I.

Example 6.--Quaterni zed copolymers of Z-vinyl pyridine and divinyl benzene A mixture of'108 cc. of freshly distilled 2-vinyl pyridine, 80 cc..of 76 mol'per cent divinyl benzene, and cc. of toluene towhich had been added'0.6 gram of 2-azo-bis- (isobutyronitrile) was cast on a'backing of glass cloth between two glass plates; The cast was baked at 80 C. for three hours, then cooled.

The cast Was then leached in absolute ethanol until equilibrium was reached, and was then heated at 60 C.

for twenty hours in a mixture of 25 parts by volume of dimethyl sulfate and 10 parts of absolute ethanol. After this treatment, whereby the N-alltyl quaternary ammonium salt of the pyridine constituent was formed, the cast membrane was washed with Water and then converted to the chloride form in a sodium chloride solution. The properties are given in Table i.

In the examples, the polymerizaticns were carried out between two glass plates The plates were approximately 20 cm. by 20 cm. and were spaced about 1 mm. apart. It has been found that under the conditions of the ex amples, substantially no evaporation takes place through the restricted aperture between the plates so that only the outermost edges of the polymerized structures lose solvent during the course of thepolyrnerization. The

"partially dried edges appear to prevent further evapora tionof solvent. After polymerization is complete, the

edges are trimmed off. In some cases, it is desirable to use sealed molds to prevent the evaporation of solvent.

It will be observed from the examples that a wide range of polymerization reactions may be carried out in the presence of a solvent for the preparation of solid gel structures, and that the ion exchange groups may be inherent in the polymerizable material or may be imparted to the gel structure by appropriate chemical treatment. Example 1 demonstrates a typical addition-type polymerization resulting in a highly crosslinked polymeric structure containing dibasic acid anhydride groups. exchange groups were formed in thispolymeric structure by hydrolysis of the anhydride groups thereby to form carboxylic groups, and the simultaneous replacement of the solvent dioxane with water then occurred.

Example 2 demonstrates another addition-type polymerization resulting in a highly crosslinked polymeric structure. Ion exchange groups were formed in the polymeric structure by sulfonating it in sulfuric acid. Before sulfonation, the solvent of polymerzation, toluene, was replaced by ethylene dichloride which was subsequently replaced by water. Example 2 thus also illustrates the use of solvent substitution. The product sulfonated in this way has improved electrochemical and mechanical properties.

Example 3 demonstrates a typical condensation polymerization of monomeric. materials, one of which con tains the sulfonic acid ion exchange group. The solvent, methanol, was replaced by water after the membranes were formed.

Example 4 demonstrates another condensation polymerization of monomeric materials containing amino ion exchange groups to form an anion exchange structure. Here again, the solvent, methanol, was later replaced by water. i

Example 5 demonstrates the formation of an anion exchange structure by an addition-type polymerization, wherein the ion exchange groups were formed on one of the monomeric precursors, 2-vinylpyridine, by the formation therefrom of the quaternary ammonium salt. After polymerization, the solvent, iso-propanol, was replaced by water.

Example 6 is similar to Example 5 except that in Example 6 the polymer was formed first, and the ion exchange groups were incorporated by the reaction of the polymeric material to form quaternary ammonium groups in it. In this example, the solvent, toluene, was first replaced by ethanol, and subsequently the membrane was treated in an ethanol solution of dimethyl sulfate to form the quaternary ammonium salt of the vinyl pyridine groups. The ethanol of the quaternized polymeric structure was thereafter replaced with water.

The solvents in which the polymerization of the reactions were carried out are typical solvents for the precursor polymerizable materials.

TABLE I Cap. nd.

Moisture, me C one. ohm ,3, Example Type percent E. M. 14. cm.

Cation (Weak). 41 2. 1 10 6 Cation 50 2. 9 11 6 "node 55 2.1 l0 7 Anion (Weak 62 4. 14 11 Anion 50 4. 2 13 .do 39 1.6 12 5 Ion 1 was determined by bringing a specimen into equilibrium with 1 N sodium hydroxide solution and then leaching repeatedly in distilled water to. remove absorbed sodium hydroxide until the leached water attained a comparatively stable pH (about 10). The specimen in this condition was then put in ten times its weight of distilled water and titrated with 0.1 N hydrochloric acid to an equilibrium pH of 5. The capacity is expressed as the number of milliequivalents of hydrogen used in the titration per 105 C. dried gram of material in the hydrogen form after correction had been made for the weight, if any, of reinforcing material. The ion exchange capacities of the structures of Examples 2 and 3 were determined by bringing specimens into equilibrium with 4 N hydrochloric acid solution, then leaching repeatedly in distilled water to remove absorbed hydrochloric acid, and finally removing all hydrogen by soaking the structures repeatedly in 4 N sodium chloride solution until equilibrium was reached and titrating the sodium chloride solution for liberated hydrogen. The capacity is expressed as the number of milliequivalents of hydrogen removed by the sodium chloride per 105 C. dried gram of material in the hydrogen form after correction had been made for the Weight, if any, of the reinforcing material.

The ion exchange capacities of the structures in Examples 4, 5, and 6 were determined by bringing specimens into equilibrium with a 4 N sodium chloride solution, then leaching repeatedly in distilled water to remove adsorbed sodium chloride and finally removing all chloride by soaking the specimens repeatedly in 4 N sodium nitrate solution until equilibrium is reached and titrating the solution for chloride. The capacity is expressed as the number of milliequivalents of chloride removed by the nitrate per 105 C. dried gram of material in the chloride form after correction had been made for the weight, if any, of the reinforcing material.

The concentration potential was measured in concentration cells with specimens separating a 0.60 N aqueous sodium chloride and a 0.30 N aqueous sodium chloride solution. The electrodes were saturated calomel electrodes connected to the sodium chloride solutions by means of saturated potassium chloride salt bridges. specimens as prepared in the examples were brought into equilibrium with 0.60 N aqueous sodium chloride solution prior to insertion in the cell. The respective solutions in the cell were continuously renewed to maintain the solution. The values recorded in Table I are the absolute values of the open circuit potential after steady conditions were attained. In such a cell, the absolute value of the thermodynamically ideal potential is 17 millivolts. It will be seen from Table I that this standard was consistently approached.

The electrical conductivity was measured by forming from a specimen as prepared according to the examples, a strip 10 cm. long, 1 cm. wide and 0.1 cm. thick, clamping the ends to copper electrodes and measuring the resistance to 60 cycle alternating current. The conductivity is the reciprocal of the resistivity, and is expressed in millimhos in Table I. The conductivity of cation structures was measured on structures in the sodium form; for anion structures, the conductivity is of the chloride form.

It will be understood that the term solvent in this specification and the appended claims refers to the solubility of the precursor polymerizable material, and not to the cured crosslinked polymers formed therefrom, since they are desirably insoluble. Similarly the term solvating liquid refers to liquid which, like solvents, will enter the polymeric structure and solvate it.

Having thus disclosed my invention, I claim as new and desire to secure by Letters Patent:

1. In the method of forming a solid electrolytically conductive, selectively permeable, unfractured ion exchange membrane having at least two dimensions in excess of 0.25 inches and comprising an insoluble infusible synthetic organic solid polymeric structure, dissociable The 1 1 ionic groups having a dissociation constant of at least 10' and being present in an amount of at least 0.3 milliequivalents per gram of solid material chemically bonded to said structure, and a solvent in gel relationship with said structure, the steps of (1) forming a dispersion in an organic solvent of material capable of polymerizing into said solid polymeric structure, (2) casting said dispersion ona reinforcing material to a membrane formhaving at least two dimensions in excess of 0.25 inches, 3) curing said dispersion to the insoluble infusible state in the presence of said organic solvent under conditions substantimly preventive of the escape of said solvent thereby forming said solid polymeric structure and (4) thereafter maintaining the solvent content of said structure.

2. The method ofclaim 1 wherein the polymeric structure is a condensation product.

3. The method of claim 1 wherein the polymeric structure is an addition product.

4. The method of claim 1 wherein the organic solvent is present to the extent of at least 25% but not more than 7 5 by weight, and wherein said dissociable ion exchange groups are of the class consisting of carboxylic, sulfonic,

quaternary amine,'and alkylene amine.

. 5. The method of claim 1 wherein the polymeric structure is a condensation product, the organic solvent is present to the extent of at least 25 but not more than 7.5% by weight and wherein said dissociable ion exchange groups are of the class consisting of carboxylic, sulfonic, quaternary amine, and alkylene amine.

6. The method of claim 1 wherein the polymeric structure is an addition product, the organic solvent is present 12 amine, and alkylene amine, under conditions substantially preventive of the loss of solvent content.

9. The'method of forming a solid electrolytically conductive, selectively permeable, unfractured ion exchange membrane having at least two dimensions in excess of 0.25 inches and comprising an insolube infusible synthetic organic solid condensation polymeric structure, dissociable ionic groups therein, and a solvent in gel relationship with said structure, the steps of (l) forming a dispersion in an organic solvent of material capable of polymerizing into said solid condensation polymeric structure, the organic solvent being present to the extent of at least but not more than 75% by weight, (2)

' casting said dispersion on a reinforcing material to a to the extent of at least 25% but not more than 75 by 7 weight and wherein said dissociable ion exchange groups are of the class consisting of. carboxylic, sulfonic, quaternary amine, and alkylene amine.

7. In the method of forming a solid electrolytically conductive, selectively permeable, unfractured ion exchange membrane having at least two dimensions in excess of 0.25 inches and comprising an insoluble infusible synthetic organic solid polymeric structure, dissociable ionic groups selected from the class consisting of carboxylic, sulfonic, quaternary amine, and alkylene amine, and being present in an amount of at least 0.3 millequivalents per gram of solid material chemically bonded to said structure, and a solvent in gel relationship with said structure, the steps of (1) forming a dispersion in an organic solvent of material containing said dissociable ionic groups and capable of polymerizing into said polymeric structure (2) casting said dispersion on a reinforcing material to a membrane form having at least two dimensions in excess of 0.25 inches and (3) curing said dispersion to the insoluble infusible state in the presence of an organic solvent under conditions substantially preventive of escape of said solvent, thereby forming said solid polymeric structure as a membrane containing said dissociable ionic groups.

8. The method of forming a solid electrolytically conductive, selectively permeable, unfractured ion exchange membrane having at least two dimensions in excess of 0.25 inches and comprising an insoluble infusible synthetic organic solid polymeric structure, dissociable ionic groups therein, and a solvent in gel relationship with said structure, the steps of (1) forming a dispersion in an organic solvent of material capable of polymerizing into said solid polymeric structure, the organic solvent being present to the extent of at least 25% but not more than 75 by weight, 2) casting said dispersion on a reinforcing material :to a membrane form having at least two dimensions in excess of 0.25 inches, (3) curing said dispersion to the membrane form'having at least two dimensions in excess ciable ionic groups of the class consisting of carboxyiic,

sulfonic, quaternary amine, and alkylene amine, under conditions substantially preventive of the loss of solvent content.

10. The method of forming a solid electrolytically conductive, selectively permeable, unfractured ion exchange membrane having at least two dimensions in excess of 0.25 inches and comprising an insoluble infusible synthetic organic solid polymeric structure, dissociable ionic groups therein, and a solvent in gel relationship with said structure, the steps of (1) forming a dispersion in an organic solvent of material capable of polymerizing into said solid polymeric structure, (2) casting said dispersion on a reinforcing material to a membrane form having at least two dimensions in excess of 0.25 inches, 3) curing said dispersion to the insoluble infusible state in the presence of said organic solvent under conditions substantially preventive of the escape of said solvent thereby forming said structure, and (4) reacting the polymeric structure with an agent capable of introducing dissociable ionic groups of the class consisting of carboxylic, sulfonic, quaternary amine, and alkylene amine, under conditions substantially preventive of the loss of solvent content. Y

11. The method of forming a solid electrolytically con ductive, selectively permeable, unfractured ion exchange membrane having at least two dimensions in excess of 0.25 inches and comprising an insoluble infusible synthetic organic solid polymeric structure, dissociable ionic groups therein, and a solvent in gel relationship with said structure, the steps of (l) forming a dispersion in an organic solvent of material capable of polymerizing into said solid polymeric structure, (2) casting said dispersion to a membrane form having at least two dimensions in excess of 0.25 inches, (3) curing said dispersion to the insoluble infusible state in the presence of said organic solvent under conditions substantially preventive of the escape of said solvent thereby forming said polymeric structure, and (4) reacting the polymeric structure with an agent capable of introducing dissociable ionic groups of the class consisting of carboxylic, sulfonic, quaternary amine, and alkylene amine, under conditions substantially preventive of the loss of solvent content.

References Cited in the file of this patent UNITED STATES PATENTS 2,223,930 Griessback Dec. 3, 1940 2,405,817 DAlelio Aug. 13, 1946 2,408,615 Dudley Oct. 1, 1946 2,409,861 Hunter Oct. 22, 1946 (Other references on following page) 13 UNITED STATES PATENTS Boyer Mar. 14, 1950 Jackson Feb. 6, 1951 Pfluger Aug. 21, 1951 Cornwell Apr. 22, 1952 Juda Apr. 28, 1953 14 OTHER REFERENCES Kunin: Ion Exchange Resins, page 62, John Wiley and Sons Inc., New York (1950).

Chemical and Eng. News, volume 29, N0. 8, February 1951, page 693. 

1. IN THE METHOD OF FORMING A SOLID ELECTROLYTICALLY CONDUCTIVE, SELECTIVELY PERMEABLE, UNFRACTURED ION EXCHANGE MEMBRANE HAVING AT LEAST TWO DIMENSIONS IN EXCESS OF 0.25 INCHES AND COMPRISING AN INSOLUBLE INFUSIBLE SUNTHETIC ORGANIC SOLID POLYMERIC STRUCTURE, DISSOCIABLE IONIC GROUPS HAVING A DISSOCIATION CONSTANT OF AT LEAST 10-5 AND BEING PRESENT IN AN AMOUNT OF AT LEAST 0.3 MILLIEQUIVALENTS PER GRAM OF SOLID MATERIAL CHEMICALLY BONDED TO SAID STRUCTURE, AND A SOLVENT IN GEL RELATIONSHIP WITH SAID STRUCTURE, THE STEPS OF (1) FORMING A DISPERSION IN AN ORGANIC SOLVENT OF MATERIAL CAPABLE OF POLYMERIZING INTO SAID SOLID POLYMERIC STRUCTURE, (2) CASTING SAID DISPERSION ON A REINFORCING MATERIAL TO A MEMBRANE FORM HAVING AT LEAST TWO DIMENSIONS IN EXCESS OF 0.25 INCHES, (3) CURING SAID DISPERSION TO THE INSOLUBLE INFUSIBLE STATE IN THE PRESENCE OF SAID ORGANIC SOLVENT UNDER CONDITIONS SUBSTANTIALLY PREVENTIVE OF THE ESCAPE OF SAID SOLVENT THEREBY FORMING SAID SOLID POLYMERIC STRUCTURE AND (4) THEREAFTER MAINTAINING THE SOLVENT CONTENT OF SAID STRUCTURE. 